Flow cytometry (flow cytometer) is generally used to analyze cells, microorganisms, and biologically-relevant particles such as liposomes (see, for example, Non-Patent Document 1). Flow cytometry is a process in which particles passing through a flow channel in a line are analyzed one by one by detecting fluorescence or scattered light emitted from each of the particles irradiated with laser light (exciting light) of a specific wavelength. Such flow cytometry can determine the type, size, and structure of individual particles by converting light detected by a photodetector into digitized electric signals and performing statistical analysis.
Some flow cytometers have the function of sorting and recovering only microparticles having specific characteristics based on the result of analysis. Particularly, a microparticle sorting device intended to sort cells is called “cell sorter”. In the cell sorter, a vibration is generally applied to a flow cell or microchip by a vibrating element or the like to convert a fluid discharged from a flow channel thereof into droplets (see Patent Documents 1 and 2).
In the cell sorter, the entry of bubbles, foreign substances, or the like into a sheath line or sample line disrupts a laminar flow or droplets, which leads to a reduction in the reliability of analysis data or a reduction in sorting accuracy and sorting purity. For example, Patent Document 3 discloses a technique about a cell sorter equipped with a bubble detector. According to this technique, bubbles present in a flow channel can be detected by a bubble detector connected to the flow channel.